Field of the Invention
The present invention relates to a bracket used to facilitate a member-to-member connection for structural load resisting systems, such as, but not limited to, seismic and progressive collapse structural load resisting systems.
Description of Related Art
A conventional brace member-to-gusset plate connection 500 is shown in FIG. 1. This type of connection has been used for many years, but is not typically implemented when seismic or other dynamic loading conditions require the connection to sustain inelastic deformation in the components connecting the brace member to the gusset plate to absorb and dissipate the dynamic forces to reduce or eliminate catastrophic failures. In the case of conventional connection 500 between a brace member 502 and a gusset plate 504 to provide lateral bracing at the intersection of a beam 510a to a column 512a, the connecting component typically comprises steel plates or hot rolled shapes such as angles or channels 506 and 508 coupled to the gusset plate 504 and configured to be bolted or welded to the brace member 502.
Another conventional structural connection 520 is illustrated in FIG. 2. Connection 520 is commonly referred to as a WT connection and has been used for many years. WT connection 520 may be used to connect a beam 510b to column 512b and uses a top WT section 522 and a bottom WT section 524 welded or bolted to the beam flanges 526a and 526b and column 512b to provide a “moment” connection or “fixed end” connection. Again, WT connection 520 is not a connection typically designed to sustain inelastic deformation in the top WT 522 and bottom WT 524 during seismic or other dynamic loading conditions. In the case of a moment connection between a beam member and column member, the WT connection typically comprises a pair of T-shaped brackets (top WT 522 and bottom WT 524) formed by cutting a wide flange (I-shaped) member usually in half, although the T-shaped brackets may be otherwise formed, such as by casting, welding, or other fabrication.
FIG. 3 illustrates a plastic WT connection 520′ which is a variation of the conventional WT connection 520 whereby the top WT section 522 and the bottom WT section 524 are shimmed with shim 528 to allow for plastic displacement of the WT sections toward or away from the face of the support column as beam 510b undergoes a rotation caused by dynamic or other forces. In the design of WT connection 520′, the top and bottom WT sections 522 and 524 are sized to be “weaker” than the beam such that rotation of the beam 510b in relation to the column 512b providing a displacement X is accommodated primarily through deformation of the WT components 522 and 524. It is known that research has shown that the portions of flange 530a of top WT section 522 and flange 530b of bottom WT section 524 which are in contact with shims 528 translate parallel to a face 532 of column 512 to accommodate relatively large deformations in the WT components 522 and 524. In addition, significant axial forces develop in the flanges 530a and 530b of the WT components 522 and 524 under large deformations which are difficult to model and estimate through analysis and design.
Thus, known and widely used conventional member-to-member connections are generally not designed to accommodate the unique forces experienced at a joint during seismic or other dynamic loading conditions which require inelastic deformation of members of the joint to absorb and dissipate the load to prevent catastrophic failure. In periods of significant seismic or dynamic loading, most existing connections result in failure and damage to the primary structural members as the connections are often designed to be stronger than the structural member itself. In such events, damage to the primary structural members would result in demolition of the frame and the supported building.
To provide some inelastic deformation in a connection, existing connections have been modified using shims to allow for inelastic deformations, but these connections have been shown to result in additional transverse loading and an unpredictable load path through the connection. This unpredictability is undesirable for structural analysts and designers as it creates an uncertainty in the capacity and performance of a structural connection.
Thus, there is a need in the art for a static structural member-to-member connection that at least (1) predictably provides a known zone of plastic deformation and capacity, (2) includes a known force distribution allowing predictability and certainty for designers, and (3) provides the point of failure so that the connection members and not the primary members experience the damage and can be replaced thereby eliminating the need to demolish an entire structure after an extreme dynamic loading event.